关于近水体下采煤防水安全煤（岩）柱保护层厚度取采高倍数问题，《建筑物、水体、铁路及主要井巷煤柱留设与压煤开采规范》（以下简称《“三下”开采规范》）附表4-3“防水安全煤（岩）柱保护层厚度”仅适用于“松散含水层”下采煤，至于基岩含水层下采煤以及老空水体下采煤如何确定保护层厚度并未涉及；常用的顶板水害风险评价技术方法评价的主要内容包括富水性评价、导通性评价、充水强度评价，在含水层富水性已知的情况下，评价方法可以进一步简化，仅评价“导通性”即可。基于以上2点，从《“三下”开采规范》出发，试图构建类似于底板突水系数那样简单的判据用于评价顶板水害风险。首先，基于“保护”一词的科学内涵，提出导水裂隙带顶界面至上覆含水层之间的隔水岩层均具有保护功能，应统称为保护层（H_b）；基于《“三下”开采规范》中保护层厚度选取采高（A）一定倍数的做法，提出了保护系数（B_s）概念，即保护层厚度与采高的比值（B_s=H_b/A）。其次，基于《“三下”开采规范》附表4-3关于防隔水煤（岩）柱保护层厚度取值的规定，提出松散含水层下采煤的保护系数分区阈值B_i=（0，2、3、4、5、6、7）；煤系地层一般为砂、泥岩互层型沉积建造，其中泥岩具有阻水功能（相当于松散层下的黏性土层），且泥岩总厚度一般大于累计采厚，故基岩含水层下保护层厚度可参照《“三下”开采规范》附表4-3“松散层底部黏性土层厚度大于累计采厚”的条件并按最大值选取，即4A，遂提出评价基岩含层的保护系数分区阈值B_i=（0，4）。根据保护系数和分区阈值，可将评价区划分为突水区（B_s≤0）、危险区（0<B_s<B_i）、安全区（B_s≥B_i）。当煤层上方有多层含水层时，应分别进行评价。最后，举例说明应用保护系数评价顶板水害风险的过程和方法，指出当含水层富水性为中等及以上时，“突水区”“危险区”的内涵侧重于安全性，通常作为防水安全煤柱留设；当含水层富水性弱或疏放经济时，“突水区”“危险区”主要用于指导疏干工程设计。

Regarding the issue of determining the thickness of the protective layer for waterproof and safe coal (rock) pillars in mining near water bodies, Appendix 4-3 of the “Code for Retaining and Mining Coal Pillars in Buildings, Water Bodies, Railways, and Main Tunnels” (hereinafter referred to as the “Three Underground Mining Code”) is only applicable to coal mining under “loose aquifers”. As for how to determine the thickness of the protective layer for coal mining under bedrock aquifers and mining under goaf water bodies, it is not involved; The main content of commonly used roof water hazard risk assessment techniques and methods includes water abundance evaluation, conductivity evaluation, and water filling strength evaluation. When the water abundance of the aquifer is known, only “conductivity” can be evaluated, and the evaluation method can be further simplified. Based on the above two points, this article attempts to construct a simple criterion similar to the coefficient of water inrush from the bottom plate to evaluate the risk of roof water damage, starting from the “Three Underground Mining Standards”. Firstly, based on the scientific connotation of the term “protection”, it is proposed that the impermeable rock layers between the top interface of the water conducting fracture zone and the overlying aquifer have protective functions and should be collectively referred to as the protective layer (H_b); Based on the practice of selecting a certain multiple of mining height (A) for the thickness of the protective layer in the “Three Lower Mining Standards”, the concept of protection coefficient (B_s) is proposed, which is the ratio of the thickness of the protective layer to the mining height (B_s=H_b/A). Secondly, based on the provisions of Appendix 4-3 of the "Three Underground Mining Specification" regarding the thickness of the protective layer for waterproof coal pillars, the threshold value of the protection coefficient zoning for coal mining under loose aquifers is proposed to be B_i=(0, 2、3、4、5、6、7); The coal bearing strata under the bedrock aquifer are generally composed of sand and mudstone interbedded sedimentary formations, where mudstone has a water blocking function (equivalent to the cohesive soil layer under the loose layer), and the total thickness of mudstone is generally greater than the cumulative mining thickness. The thickness of the protective layer can be selected according to the condition of “the thickness of the cohesive soil layer at the bottom of the loose layer is greater than the cumulative mining thickness” in Appendix 4-3 of the “Three Underground Mining Specifications” and selected according to the maximum value, Therefore, the threshold value of the protection coefficient zoning for evaluating the bedrock aquifer is B_i=(0,4). According to the protection coefficient and zoning threshold, the evaluation area can be divided into water inrush zone (B_s≤0), danger zone (0<B_s<B_i), and safety zone (B_s≥B_i). When there are multiple aquifers above the coal seam, separate evaluations should be conducted. Finally, an example is given to illustrate the process and method of applying protection coefficient to evaluate the risk of roof water damage. It is pointed out that when the water content of the aquifer is medium or above, the connotation of “water inrush zone” and “dangerous zone” focuses on safety and is usually reserved as waterproof safety coal pillars; When the aquifer has weak water abundance or is economically drained, the “water inrush zone” and “dangerous zone” are mainly used to guide the design of drainage engineering.